1. Field of the Invention
The present invention relates to an optical fiber mounting waveguide device and a method for fabricating the same in which an optical connection loss is small, and productivity is high.
2. Related Art
Conventionally, in a waveguide device on which an optical fiber is mounted (hereinafter, referred as “optical fiber mounting waveguide device”), an optical fiber groove for guiding an optical fiber on an extended line of a core and easily fixing the optical fiber stably.
The optical fiber mounting waveguide device is provided with end surfaces of a cladding and the core facing to the optical fiber mounting groove. In other words, the cladding is provided with a stepped portion, and a bottom part of the stepped portion is provided as a bottom surface of the optical fiber groove, so that an end surface of the optical fiber mounted in the optical fiber groove contacts with the end surfaces of the cladding and the core.
Japanese Patent Application Laid-Open No. 2006-184754 (JP-A-2006-184754) and Japanese Patent Application Laid-Open No. 2002-267860 (JP-A-2002-267860) disclose the conventional optical fiber mounting waveguide devices.
FIG. 4 is a plan view of an optical fiber mounting waveguide device in a first conventional example.
As shown in FIG. 4, the conventional optical fiber mounting waveguide device 101 comprises an optical fiber groove 102 for mounting an optical fiber 105, a cladding 103, a core 104 surrounded by the cladding 103 and formed until an end surface of the cladding 103, in which an end surface of the optical fiber 105 mounted in the optical fiber groove 102 contacts with the end surface of the cladding 103, so that a core (not shown) of the optical fiber 105 is optically coupled to the core 104 in the optical fiber mounting waveguide device 101.
FIG. 5 is a partially enlarged view of the conventional optical fiber mounting waveguide device shown in FIG. 4.
FIG. 5 shows an enlarged plan view of a portion in vicinity of the end surface of the cladding 103. A tip portion 104a of the core 104 has roundness as shown in FIG. 5. The roundness of the end surface of the cladding 103 is formed as follows. For example, when the optical fiber mounting waveguide device 101 is fabricated by photolithography technique (direct exposure), a photomask is provided for the exposure on a base waveguide substrate so that the core 104 and the cladding 103 are formed to be defined in a desired configuration on the base waveguide substrate. At this time, for example, a diffraction of light may occur at edges of the photomask, so that a mask pattern that is right angle-edged on the photomask is exposed with the roundness. Even if a core pattern in the photomask is right angle-edged, since the end surface of the cladding 103 is located at the edge of the photomask, the tip portion 104a of the formed core 104 has the roundness. In particular, the roundness is easily formed at the tip portion 104a of the core 104, when a core diameter (core size) is small.
In addition, a space between the tip portion 104a having the roundness of the core 104 and an end surface 103a of the cladding 103 is filled with the cladding 103.
When the tip portion 104a of the core 104 has the roundness as shown in FIG. 5, the cladding 103 intrudes a gap between a curved surface of the tip portion 104a of the core 104 and the optical fiber 105, so that an interface between the core 104 and cladding 103 is curved. As a result, an optical path is changed due to the refraction of the light, and the light significantly leaks in adjacent cores, so that an optical isolation is deteriorated and an optical connection loss is increased.
In addition, when the tip portion 104a of the core 104 has the roundness and is covered by the cladding 103, an optical coupling property is greatly changed in accordance with a relative position (a position in an orientation along the end surface) of the core 104 with respect to the optical fiber 105, so that a dispersion in the loss due to variation of the relative position (the orientation along the end surface) between the core tip portion 104a and the optical fiber caused by manufacturing dispersion. As a result, the productivity of the optical fiber mounting waveguide device is decreased.
FIG. 6 is a cross sectional view of an optical fiber mounting waveguide device in a second conventional example.
In the optical waveguide device disclosed by JP-A-2002-267860, there is a problem in that the core end surface has the roundness as described above so that the optical connection loss is increased in the connection with the optical fiber. Further, as shown in FIG. 6, according to this method, an optical connection end surface of a core 61 is formed in a concave portion of a cladding 62. Thereafter, a cladding material and a substrate covering the optical connection end surface are removed to provide an optical waveguide in which the core 61 is protruded from a cladding end surface. Therefore, there is a problem in that the core 61 is damaged during the removal process of the cladding 62.